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CE 356: Fundamentals of Environmental Engineering

Learning Objectives. Comprehend basic characteristics of domestic wastewater (flow rate, BOD, SS) and apply these characteristics to a preliminary engineering design.Calculate mass loadings within the wastewater treatment system for BOD and SS.Calculate and interpret mass balances for mixtures of wastewaters.Calculate and interpret population equivalents for industrial wastewater..

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CE 356: Fundamentals of Environmental Engineering

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    1. CE 356: Fundamentals of Environmental Engineering Wastewater Characteristics Ricardo B. Jacquez Professor, CAGE Department New Mexico State University Teaching Assistant: M. T. Myint

    2. Learning Objectives Comprehend basic characteristics of domestic wastewater (flow rate, BOD, SS) and apply these characteristics to a preliminary engineering design. Calculate mass loadings within the wastewater treatment system for BOD and SS. Calculate and interpret mass balances for mixtures of wastewaters. Calculate and interpret population equivalents for industrial wastewater.

    3. Wastewater Characteristics Sources of Wastewater Physical Characteristics Sewer Crown Corrosion Chemical Characteristics Typical composition of untreated domestic wastewater Biological Characteristics Population Equivalents

    4. Sources of Wastewater (Major Components) Domestic: food, soap and detergents, bathroom (fecal and urine), and paper. Commercial: bathroom and food from restaurants and other “stores.” Industrial: highly variable, dependent on industry, controlled by pre-treatment regulations. Runoff from streets: sand and petroleum and tire residues (infiltration, not a direct discharge).

    5. Wastewater Characteristics Characteristics are categorized as: Physical Chemical Biological Concentrations characterize wastewater as: weak, medium, and strong.

    6. Physical Characteristics Solids - Total solids: residue after evaporating all water (50% volatile and 50% fixed) (Volatile=organic. Fixed=inorganic mg/L) - Suspended solids: residue retained on a filter (75% volatile and 25% fixed). - Dissolved solids: residue passing through a filter (40% volatile and 60% fixed). - Settleable solids: residue after one hour settling in an Imhoff cone (ml/L) (the indicator of primary sludge).

    8. Physical Characteristics cont. Odors: Odors are caused by gases produced by anaerobic decomposition of wastewater (driven by microorganisms and limited oxygen). Aerobic Respiration: Organics + O2* = CO2 + H2O Anaerobic Respiration: Organics + SO4-2 * = H2S + odorous organics Fermentation: Organics + Reduced Organics * = odorous organics * Electron Acceptor Various odorous compounds result

    10. Sewer Crown Corrosion - Organics+SO4-2 =H2S + odorous organics H2S is volatile, rises to the crown of sewer, and dissolves in water vapor. Crown is aerobic (O2). H2S + 2O2 = H2SO4 (Bacteria ? sulfuric acid) Crown caves in, expensive prevention and sewer maintenance / replacement. water condensation Aerobic H2S + 2O2 = H2SO4 SO-2 H2S Anaerobic

    11. “SEWAGE” Domestic wastewater is the ideal mixture of biodegradable nutrients and microorganisms: BOD (organics) Nitrogen (N) Phosphorus (P) Miscellaneous Micronutrients (S, Fe, Ca, . . . ) Bacteria

    12. Chemical Characteristics Organics: Predominant biodegradable fraction, BOD -Protein -Fats, Oils, and Greases -Carbohydrates -Surfactants (detergents) -Urea Priority pollutants Industrial solvents, pesticides, etc. Pre-treatment standards control concentrations to trace levels

    13. Chemical Characteristics cont. Inorganic Matter Nitrogen: from protein and urea. NH2, NH3, NH4+ forms ammonia and organics. An essential nutrient for growth of bacteria. Oxygen Demand: NH4+ + 2O2 = NO3- + 2 H+ + H2O

    14. Chemical Characteristics cont. Phosphorous: phosphate (PO4-3) Inorganic-detergents organic-food and metabolic wastes Trace nutrients: S, Fe, Mn, Mg, Ca, K, Zn, Mo, etc. . . . . . plentiful

    20. Mass Loading Calculations Mass = Conc x Flow Rate = mg/L x MGD x 8.34 x 1/24 = lbs/hr Mass = Conc x Flow Rate = mg/L x ft3/sec x 0.22 = lb/hr

    21. Mass Balance Calculations Fundamental Law: Massin = Massout Massin = Q1 x Conc1 + Q2 x Conc2 (knowns) Massout = QT x ConcT (unit constants cancel out) QT = Q1 + Q2 ConcT = unknown

    22. Biological Characteristics “Most” microorganisms known to microbiologists can be found in domestic wastewater. Bacteria Protozoa Viruses Algae (limited)

    23. Population Equivalents 1. Wastewater discharge: 100 -120 gpcd - 70 gpcd domestic - 10 gpcd industrial/commercial - 20 to 40 gpcd infiltration 2. Suspended Solids and BOD SS = 0.2 lb pcd (without kitchen grinder) SS = 0.22 lb pcd (with kitchen grinder) BOD = 0.17 lb BOD pcd BOD = 0.26 lb BOD pcd (with kitchen grinder)

    24. Population Equivalents cont.

    26. Population Equivalents cont. Used to Establish population equivalency of an industrial waste. Establish charge for treating industrial waste based on BOD or SS rather than flow.

    28. Summary Domestic wastewater is a well balanced, nutrient rich medium for bacterial decomposition. After primary treatment, biodegradation is the most cost effective secondary treatment. - Effective biodegradation requires BOD:N:P = 100:5:1 - Domestic wastewater contains 100:20:5. - Organics (BOD) limits N and P reduction. Advanced treatment is required to remove excessive N and P.

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